Sound-reproducing apparatus



April 29, 1930. LE ROY WISTAUNTON I 1,756,838

SOUND REPRCDUCING APPARATUS Filed Jul 3, 132a 2""i 1 j F19. 2 20 fig. r1 5 42 $4 &

.K 7 1 k INVENTOR.

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W 4 ATTORNEYS.

Patented Apr. 29, 191 50 uNrrEo STATES PATENT OFFICE LE ROY W. STAUNTON, OF NEW YORK, N. Y., ASSIGNOR OF ONE-HALF TO STEPHEN BOURNE, OF NEW YORK, N. Y.

SOUND-RELRODUCING APPARATUS Application filed July 3,

This invention relates to sound-reproducing apparatuses and particularly to apparatuses which employ (liaphragms adapted to be actuated in response to a sound-controlled electric current for setting up vibrations in the free air. Such apparatus is adapted to be used, for example, as a loud speaker in of. normal audibility without the aid of resonators and utilize sheet diaphragms so that they.may be made into disk types of loud speakers when desired. 1

Other objects of the invention willin part be obvious and will in part appear herein- 7 after.

The invention accordingly comprises the features of construction, combinations of elements, and arrangement of parts, whlclr will be exemplified in the constructions hereinafter set forth and the scope of the application of which will be indicated in the claims.

- For a fuller understanding ofthe nature and objects of the invention reference should he had to the following detailed description taken in connection with the accompanying drawing, in which Fig. 1 shows a vertical cross-section of a sound-reproducing device constructed in accordance with the invention;

Fig. 2'shows 'a similar cross-section of a modified form thereof;

Fig. 3 isa front elevation of another modified form;

Fig. t is a fragmentary view showing a detail thereof; and I Fig. 5 is a detailed view of a modified form of' diaphragm suitable for use in loud speakers, constructed in accordance with the present invention.

1926. Serial No. 120,414.

Referring now to thedrawing, and particularly to Fig. '1, 10 denotes a frame or other suitable support which is constructed to be relatively non-resonant to the sounds repro- 'duced'by the sound-producing element, here shown as diaphragm 11 clamped between the support 10 and a clamping ring 12, the latter being bolted or otherwise secured to the support 10. The support 10, for convenience, is shown as mounted on a pedestal 13; it will be understood, however, that the frame 10 may be supported in any convenient manner and may be built into radio receiving sets if desired.

The diaphragm 11 is shown as a laminated structure composed of a basic sheet 11, whose edges extend to and are secured in the frame 10, and a plurality of superposed sheets or layers 14 of successively decreasing diameter as the centre is approached. The layers 14 are adhesively secured to the basic sheet ll and to each other, so as to form a unitary diaphragm structure of gradually increasing thickness toward the centre. -A- polarized relay is shown at 15 mounted in the frame 10 having its vibrating arm 16 positively connected through the rod 17 for driving or vibrating the diaphragm. The rod 17, as indicated, is preferably adjustably secured in a threaded sleeve 18 which is secured 1n and passes through all the laminations of the diaphragm.

It is thus seen that, when connected to be traversed by a sound-controlled electric current, for example the current from an audio-stage of a-radio receiving set, the diaphragm 11 will be driven or forced into vibration in response to the variations in diathe sound-controlled current. I The phragm in consequence .is set into vibration at a frequency corresponding to the sound produced variations of'the current.

In order that this construction shall be adapted for reproducing the vibrations of the original sound so as.to have an amplitude of,

normal audibility, thediaphragm 1'1, in accordance with. the present invention is of the relay 15 is sheet material and has such elastic properties that the centre ofthe diaphragm or point from which the diaphragm is driven is approximately always a loop, while the edges of the diaphragm are a node, for the average frequency of audible sounds. This requires that the diaphragm itself should have a diameter equal to. approximately one-half the average wave-length, whereby the radius is approximately one quarter of the average wave-length. In this way a relatively large diaphragm other than the edges; since such nodal points would represent an annulus of inactive surface, while addition, the portions of the surface at. each side of the annulus are in opposite phases and will in consequenceIstill further reduce the active area of the diaphragm and the consequent ampliture of the soundwhich it is .desired to reproduce. The sheet material, suita le for the construction of the diaphragm 11 atpresent generally-available, are the relatively thin and stiff sheetmaterials, such as sheet metal,

sheet fibre, parchment paper, parchment and external.

the like; these however, in their normal state, do not; possess the proper elasticity.

It has been ascertained that the required degree of elasticity can be imparted by giving the diaphragm material a permanent stress,

which is mainly internal but may be partly Sheet metal, for example, sheet steel, may be given a permanent stress of the character desired by heating the sheet substantially uniformly until it has expanded substantially uniformly over its entire surface. The expanded sheet, while hot, is then placed over a die or other support which is the shape of the frame 10 on which the diaphragm is to be mounted when on the die, the sheet is drawn and cooled. When cooled in the drawn condition; will have a permanent internal stress, which may be added to externally when placed in the frame of the loud speaker.

' Parchment paper has been found to be well adapted to the taking up of a permanent internal stress by wetting, stretching, and dry-- ing the same; this may be accomplished, for example, by stretching the parchment, when thoroughly Wet, substantially uniformly in all directionsupon a frame and drying the same while under the stretching tension. The material when dry is found to be permanently internally stressed, is stiff, and has difierent elastic properties than originally, and when put in the frame 10 may be further externally stressed by the tension employed by the supporting frame. It is convenient,

' however, in the. practice of the present invention to employ the frame itself in the process of manufacture as the stretching means for parchment paper, when it is the material of the diaphragm, since the laminated diaphragm may be placed therein while ,wet, and clamped in place. i

By thus permanently stressing the dia phragm material the desired elasticity results, and a disk type of loud speaker in consequence is provided which sets up sounds of normal audibility directly in the free air. Av

a varnish which does not have an oilbase, for-- example, a cellulose varnish such as-is, now frequently used for varnishing the fuselage and the like of airplanes.

A construction adapted for the production of a large volumeof sound is shown in Fig. 2. Here a pair of diaphragms 21 are mounted in the frame 20 back to back. In this instance the central lamination 24 of the diaphragms is of magnetic material, for example, an iron disk; and is adjustably. securedsubstantially at the centre of the diaphragm. These magnetic laminations are adapted to be disposed a proper distance from the pole piece 25 of the actuating electromagnetic winding 26'. y

While the magnetic lamination 24 is centrally disposed on the exterior of the back side of each of the diaphragms 21, the magnetic material for actuation in this arrangement is not necessarily so disposed and can be disposed at any point within the dia-' phragm construction. It has also been ascertained that 'while the diaphragms will in general be constructed as circular that other shapes may be equally well employed, for example, elliptical and relatively square and oblong shapes. In; Fig. 3 a loud speaker is shown in which a relatively square diaphragm 31 is shown as mounted in a frame 30. The

connection for the driver is indicated at'34. This point, as shown is not the central point of the diaphragm 31. In this instance the driver is purposely connected at a point somewhat ofl centre, since it is found that the driver may be connected at points somewhat to one side of the centre with advantageous results in certain instances. The apparent reason for this is that such an eccentric position of the driver permits the'setting up of certain overtones which are not disadvantageous.

phragms in Figs. 1 and 2 are adapted to apply power for vibrating the same from only one ten ' ence.

side, it is frequently advantageous to'provide for a balanced driving effect. To this end the driver 34 is preferably divided into two parts 34' and 34 and placed on the opposite sides of the diaphragm 31, as indicated in Fig. 4,

the windings being electrically so arranged that their driving eflects are 180 out of phase, whereby there is produced a balanced driving effect on the two opposite sides of the diaphragm.

While the result of the present invention. it has been ascertained, depends substantially entirely upon the elastic properties imparted by stressing the diaphragm material, still, in order that it maybe set into vibration from a relatively central point so that substantially the whole of its surface is active and the central point a loop and the edges thereof a node, it. should be constructed so that the vibration-wave travels with uniform velocity from the centre to the edges, and to this end should have its mass decreased radially. The mass is consequently greatestat the centre and is gradually decreased outwardly. This arrangement is attained in substantially any convenient manner. The diaphragm 11 in Fig. 1 is shown as achieving this construction by having adhesively secured the laminations of successively decreasing diameters to the basic sheet 11. Yet this result may be secured by securing the laminations on both sides. -A convenient manner of accomplishing this is shown in Fig. 5 where a cross-section of the laminated diaphragm is shown at 41 where the diaphragm is substantially lenssha ed, the central sheet, however, being exdedsto form a rim 2 about the circumfer- Sincecertain changes may be made in the above construction and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In sound-reproducing apparatus, the combination with a substantially non-resonant support, of a dia hragm mounted in a state of relatively higi permanent internal stress on said support, 'sa-id diaphragm being a composite laminated structure comprising superposed layers of sheet material, the successive layers to be adhesively secured and of successively decreasing diameters toward the centre, and .means arranged to vibrate said diaphragm, whereby vibrations are produced in said diaphragm of sufficient amplitude for reproducing sound of normal audibility directly in the surroundingfree air independently of resonators.

2. In sound-reproducing apparatus, the combination with a substantially. non-resonant support, of, a dia )hragm mounted in a state of relatively higlipermanentinternal stress on said support and stressed externall v, said stresses being of a character adapted to impart a resiliency sutficientto enable it to reproduce soundsdof normal audibility directly in the surrounding free air, said diaphragm being composed of superp osed laminations of successively decreasing diameters toward the centre, said lan'linations being secured together so as to produce a rela tively unitary diaphragm construction, and

means arranged for vibrating said diaphragm so as to'have its centre substantiallyalways a loop and its' periphery always a node.

3. In sound-reproducing apparatus, the combination with a substantially non-resonant support, of a dia. hragin mounted in a state of relatively high permanent internal stress on said support, and stressed externally, said stresses being adapted to impart an elasticity such that the diaphragm when having a diameter of approximately half a wavelength of the average audible soundwvave, will set up vibrations in the surrounding free air of suflicient amplitude for normal audibility without the aid of resonators, said diaphragm being composed of superposed laminations of successively decreasing diameters toward the centre, said laminations being secured together so as to produce a relatively unitary diaphragm construction, and means arranged for vibrating said diaphragm so as to have its centre substantially always a loop and its periphery always a node.

.4. In -'sound-reproducing apparatus, the

combination with a substantially non-reso-.

nant support, of a laminated diaphragm mountedin a state of relatively high permanent internal stress on said support, and stressed externally, such stresses being of a character adapted to impart an elasticity to said diaphragm such as to enable it to reproduce sounds of normal audibility directly in the surrounding free air and havinga structure of greater mass at the centre and decreasing outwardly toward the edges so as to propagate sound therein with a uniform velocity in substantially all radial directions from said centre, and means arranged to vibrate said diaphragm and to drive it from a point substantially at said centre.

5. In sound-reproducing apparatus, the combination with a substantially non-resonant support, of a laminated diaphragm mounted in a state of relatively high permathe surrounding free air and having a structure of greater mass at the centre and decreasing outwardly toward-the edges so as to propagate sound therein with a uniform velocity in substantially all radial directions from said centre, and means, arranged to provide a balanced driving effectfor said diaphragm connected to drivethe same substantially from said centre.

6. In sound-reproducing apparatus, the combination with a substantially non-resonant support, of a laminated diaphragm mounted in a state of relatively high permanent internal stress on'said support, and stressed externally, such stresses being of a character adapted to impart an elasticity to I said diaphragm such as to enable it to reproduce sounds of normal audibility directly in the surrounding-free air and having a structure of greater mass at thecentre and decreasing. outwardly toward the edges so as to propagatesound therein with a uniform velocity 1n substantlally all radial dlrections from said centre, and means arranged to'drive said diaphragm from a point adapted to pro duce unobj ectionable overtones.

I 'ln testimony whereof I afiix my signature. 

